in a 90 legacy is there a way of testing your knock sensor while driving. as my old auto instructor would call it, to see if it's singing. I think i might need to bump up to the next grade of gas. i just replaced it with a new one because the old one was all sorts of cracked up.

 

as far as i know how they work if it hears a knock it makes a small amount of electricity. is this something i could hook a volt meter up to and read or would i need something more precise like an oscilloscope.

Your best option would be to build this scan tool

http://www.graphics.cornell.edu/~v/b10scan/

 

It allows you to monitor the ECU, which includes an option for pinging/knock.

 

There's a thread with more info on the scan tool in the electrical forum on www.bbs.legacycentral.org